The Buffy Verse where Xander was Born with the gift of Power Immunity -  User is immune to all or certain supernatural powers and effects, although indirect attacks can still effect the user

• Ability Resilience - Immune to superpower manipulation-based attacks.

• Elemental Immunity - Immune to element-based attacks and abilities.

• Evil Immunity - Immune to becoming or to anything that's pure evil.

• Fate Immunity - Immune to the forces of Causality and Fate

• Illusion Awareness - See through illusions.

• Life Resilience - Immune to Death Manipulation.

• Magic Immunity - Immune to magic.

• Panmnesia - Immune to memory manipulating abilities.

• Paranormal Immunity - Immune to paranormal-based attacks, abilities and effects.

• Precognitive Immunity - Can't be seen in precognitive-based abilities.

• Psychic Shield - Immune to telepathic, empathic and mental abilities.

• Reality Anchoring - Immune to reality manipulation-based abilities.

• Seduction Immunity - Immune to seductive love, lust and sex-based abilities.

• Semi-Immortality - Immune to aging-based abilities.

• Shapeshifting Awareness - See through a shapeshifters disguise.

• Soul Anchoring - Immune to Soul-affecting powers.

• Temporal Protection - Immune to alterations of the timeline changing.

• Temporal Immunity - Immune to temporal-based powers

• How much different would everything be? Would Xander still be as close to Willow if he wasn't as effected by the Hellmouth and didn't constantly forget/ignore the deaths & various strangness? How would Willow react when every spell she decides to cast on her Xander toy failed? What if it allowed him to save a would have been forgotten little brother, that he loved & protected unconditionly, by allowing him to see past Illusions/shapeshifting abilities...etc of his would be killer?